Hormones are long-distance signaling molecules that target distant organs to regulate various physiological functions. They can be classified into several major types based on their structure and function:
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Steroid Hormones:
- Steroid hormones have a core structure of four carbon rings.
- Examples include testosterone, estrogen, progesterone, and vitamin D.
- They are lipid-soluble, allowing them to cross cell membranes and directly influence gene expression by interacting with receptors in the cell nucleus 1 2 3.
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Peptide Hormones:
- These hormones consist of short chains of amino acids.
- They are not lipid-soluble and cannot cross cell membranes, so they bind to surface receptors and trigger signal transduction cascades inside the cell.
- Examples include insulin and growth hormones 2 4.
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Polypeptide Hormones:
- Similar to peptide hormones but consist of longer chains of amino acids.
- They also bind to cell surface receptors and initiate a series of intracellular reactions 2.
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Amino Acid-Based Hormones:
- These hormones are derived from single amino acids.
- Examples include thyroid hormones (derived from tyrosine), norepinephrine, dopamine (based on tyrosine), and serotonin (derived from tryptophan).
- They perform a variety of functions, spanning neurotransmission and metabolic regulation 1 5.
Understanding these different classes of hormones helps in grasping how the endocrine system operates, including the varied ways they interact with their target cells and regulate body functions.
